Battery protection circuit

ABSTRACT

A battery protection circuit includes a voltage source, a first resistor, a charging controller, a first charging transistor, a second resistor, and a current voltage converter. The first resistor includes a first terminal connected to the voltage source. The charging controller supplies a charging control current through a charging control terminal. The first charging transistor includes a gate terminal and a first terminal. The second resistor is connected between the gate terminal and first terminal of the first charging transistor. The current voltage converter is connected to a second terminal of the first resistor to electrically connect the voltage source to the gate terminal of the first charging transistor depending on the charging control current.

CROSS-REFERENCE TO RELATED APPLICATION

Korean Patent Application No. 10-2016-0002271, filed on Jan. 7, 2016,and entitled: “Battery Protection Circuit,” is incorporated by referenceherein in its entirety.

BACKGROUND

1. Field

One or more embodiments described herein relate to a battery protectivecircuit.

2. Description of the Related Art

A battery protection circuit protects a battery cell from ashort-circuit, disconnection, over-current, over-voltage, or anothertype of malfunction that may occur, for example, during charging and/ordischarging operations. One type of battery protection circuit includesa charging and discharging controller (e.g., a battery integratedcircuit (IC)) to perform various battery protection operations.

A relatively inexpensive battery protection circuit includes a non-smartbattery IC. This kind of IC may exclusively perform a protectionfunction without a micro controller unit (MCU). This type of IC mayemploy an open-drain-type current source method under control of acharging transistor in attempt to reduce power consumption. However,this and other types of battery protection circuits have drawbacks.

SUMMARY

In accordance with one or more embodiments, a battery protection circuitincludes a voltage source; a first resistor including a first terminalconnected to the voltage source; a charging controller to supplycharging control current through a charging control terminal; a firstcharging transistor including a gate terminal and a first terminal; asecond resistor connected between the gate terminal and first terminalof the first charging transistor; and a current voltage converterconnected to a second terminal of the first resistor to electricallyconnect the voltage source to the gate terminal of the first chargingtransistor depending on the charging control current.

The battery protection circuit may include a second charging transistorhaving a gate terminal and a first terminal; and a third resistorconnected between the gate terminal and the first terminal of the secondcharging transistor, wherein a second terminal of the second chargingtransistor is electrically connected to the first terminal of the firstcharging transistor, and wherein the gate terminal of the secondcharging transistor is electrically connected to the gate terminal ofthe first charging transistor.

The current voltage converter may include a first transistor including afirst terminal electrically connected to a second terminal of the firstresistor; a second transistor including a first terminal electricallyconnected to a second terminal of the first transistor; and a fourthresistor including a first terminal electrically connected to a secondterminal of the second transistor and a second terminal electricallyconnected to the gate terminals of the first and second transistors andthe charging control terminal. The voltage source may include acapacitor, and the capacitor may be electrically connected to positiveelectrode of a battery cell to maintain a voltage. The chargingcontroller may include a power-supply terminal, and the chargingcontroller may receive power from the voltage source through thepower-supply terminal to generate the charging control current. Thevoltage source may include a diode and a fifth resistor.

A first terminal of the power-supply terminal and the first terminal ofthe first resistor may be electrically connected to a first terminal ofthe capacitor. The first transistor may be enabled when the chargingcontrol current is in an on level and the first and second chargingtransistors are enabled. The second transistor may be enabled when thecharging control current is in an off level and the first and secondcharging transistors are disabled. The second resistor may have aresistance value greater than that of the fourth resistor. The secondresistor may have a resistance value greater than that of the firstresistor.

In accordance with one or more other embodiments, a battery protectioncircuit includes a first resistor connected to a voltage source; a firstcharging transistor connected to a battery terminal; a second resistorconnected to the first charging transistor; a controller connected tothe voltage source to supply charging control current; and a converterto connect the voltage source to the first charging transistor based onthe charging control current, wherein the first resistor has aresistance value less than the second resistor and wherein a timeconstant of the first charging transistor is based on the resistancevalue of the first resistor.

The battery protection circuit may include a second charging transistor;and a third resistor connected to the second charging transistor,wherein gate terminals of the first and second charging transistors areconnected to the converter. The resistance value of the first resistormay be less than a resistance value of the third resistor. The convertermay include a first transistor connected to the first resistor; a secondtransistor connected between the first transistor and the second andthird resistors; and a fourth resistor connected between the controllerand gate terminals of the first and second transistors.

BRIEF DESCRIPTION OF THE DRAWINGS

Features will become apparent to those of skill in the art by describingin detail exemplary embodiments with reference to the attached drawingsin which:

FIG. 1A illustrates an embodiment of a battery protective circuit, andFIG. 1B illustrates another embodiment of a battery protective circuit;and

FIGS. 2A and 2B illustrate other types of battery protective circuits.

DETAILED DESCRIPTION

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawings; however, they may be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey exemplary implementations to those skilled in the art. Theembodiments may be combined to form additional embodiments.

In the drawings, the dimensions of layers and regions may be exaggeratedfor clarity of illustration. It will also be understood that when alayer or element is referred to as being “on” another layer orsubstrate, it can be directly on the other layer or substrate, orintervening layers may also be present. Further, it will be understoodthat when a layer is referred to as being “under” another layer, it canbe directly under, and one or more intervening layers may also bepresent. In addition, it will also be understood that when a layer isreferred to as being “between” two layers, it can be the only layerbetween the two layers, or one or more intervening layers may also bepresent. Like reference numerals refer to like elements throughout.

FIG. 1A illustrates an embodiment of a battery protective circuit 10which includes a voltage source 100, a charging controller 200, acurrent voltage converter 300, a first charging transistor 410, a firstresistor R1, and a second resistor R2. The battery protective circuit 10may further include a second charging transistor 420 and a thirdresistor R3 in order to prepare for an operation fail of the firstcharging transistor 410.

The battery protective circuit 10 is electrically interposed between abattery cell 20 and a charger 30 to protect the battery cell 20 fromshort-circuit, disconnection, over-current, over-voltage, or the like,that may occur during charging and discharging of the battery cell 20.In the battery protective circuit 10 of the present exemplaryembodiment, portions related to charging control are selectivelyillustrated. The battery protective circuit 10 may further include acircuit configuration for performing another protective function. Forexample, the battery protective circuit may further include a dischargetransistor, a fuse, a current/voltage sensing unit, and/or the like.

The voltage source 100 may supply voltages for operating the chargingcontroller 200 and the current voltage converter 300. The voltage source100 may supply a voltage to a power supply terminal Vcc of the chargingcontroller 200 to allow for operation of the charging controller 200.The voltage source 100 may supply a voltage to the current voltageconverter 300 through the first resistor R1, and the current voltageconverter 300 may apply a voltage to gate terminals of the firstcharging transistor 410 and the second charging transistor 420.

The first resistor R1 has a first terminal connected to the voltagesource 100. A second terminal of the first resistor R1 is connected tothe current voltage converter 300. Enable speeds and disable speeds ofthe first and second charging transistors 410 and 420 may be determinedaccording to a resistance value of the first resistor R1. This will bedescribed in detail with reference to FIG. 1B. In one embodiment, theresistance value of the first resistor R1 may be smaller than that ofthe second resistor R2 or the third resistor R3.

The charging controller 200 supplies a charging control current I200 tothe current voltage converter 300 through a charging control terminalCHG. The charging controller 200 may be a battery IC and may not includea micro controller unit to reduce costs. Further, the chargingcontroller 200 may employ an open-drain-type current source method toreduce or minimize power consumption. The charging control current I200may have an on level or an off level. For example, the charging controlcurrent I200 may be, for example, 6 uA in the case of an on level. Whenthe charging controller 200 opens the charging control terminal CHG, thecharging control current I200 may be in the off level by high impedance.The charging controller 200 may receive power from the voltage source100 through the power supply terminal Vcc in order to generate thecharging control current I200.

The second resistor R2 is connected between a gate terminal and a firstterminal of the first charging transistor 410. The gate terminal of thefirst charging transistor 410 is connected to an output terminal of thecurrent voltage converter 300. The second resistor R2 serves as apull-down resistor for preventing the voltage of the gate terminal ofthe first charging transistor 410 from falling in an undefined state.The first terminal and a second terminal of the first chargingtransistor 410 may be electrically connected, for example, to a negativeelectrode of the battery cell 20. In one embodiment, the first chargingtransistor 410 may be, for example, between opposite ends of batterycell 20.

The third resistor R3 is connected between a gate terminal and a firstterminal of the second charging transistor 420. The gate terminal of thesecond charging transistor 420 is connected to the output terminal ofthe current voltage converter 300. The third resistor R3 serves as apull-down resistor for preventing a voltage of the gate terminal of thefirst charging transistor 420 from falling in an undefined state. Thefirst terminal and a second terminal of the second charging transistor420 may be electrically connected to the negative electrode of thebattery cell 20. In one embodiment, the second charging transistor 420may be between opposite ends of the battery cell 20. The second terminalof the second charging transistor 420 may be connected in series to thefirst terminal of the first charging transistor 410.

The current voltage converter 300 is connected to the second terminal ofthe first resistor R1 and electrically connects the voltage source 100to the gate terminals of the first and second charging transistors 410and 420 depending on the charging control current. For example, when thecharging control current is at the on level, the current voltageconverter 300 applies the voltage of the voltage source 100 to the gateterminals of the first and second charging transistors 410 and 420 toenable the first and second charging transistors 410 and 420. When thecharging control current I200 is at the off level, the current voltageconverter 300 disables the first and second charging transistors 410 and420 by blocking the voltage of the voltage source 100.

In the exemplary embodiment of FIG. 1A, the charging control currentI200 is converted to a voltage signal by the current voltage converter300. The voltage signal is applied to the gate terminals of the firstand second charging transistor 410 and 420, instead of directly applyingthe charging control current to the charging transistors. Accordingly,the first resistor R1 is exclusively considered, without considering thesecond and third resistors R2 and R3, in order to obtain time constantsof the first and second charging transistors 410 and 420. Therefore, itis possible to secure the enable speed and disable speed of the firstcharging transistor 410 by appropriately adjusting the resistance valueof the first resistor R1.

FIG. 1B illustrates a more detailed embodiment of the battery protectivecircuit in FIG. 1A. Referring to FIG. 1B, an exemplary circuit of thevoltage source 100 and the current voltage converter 300 is illustrated.

The current voltage converter 300 includes a first transistor TR301, asecond transistor TR302, and a fourth resistor R4. The first transistorTR301 may be a NPN transistor, and a first terminal and a secondterminal thereof may be respectively connected to the second terminal ofthe first resistor R1 and a first terminal of the second transistorTR302. The second transistor TR302 may be a PNP transistor and a firstterminal thereof may be connected to the first transistor TR301. Asecond terminal of the second transistor TR302 may be electricallyconnected to the first terminal of the fourth resistor R4 and thenegative electrode of the battery cell 20. A second terminal of thefourth resistor R4, a gate terminal of the first transistor TR301, and agate terminal of the second transistor TR302 are connected to thecharging control terminal CHG. In one embodiment, the fourth resistor R4and the second resistor R2 may have different resistance values, e.g.,the fourth resistor R4 may have a resistance value less than that of thesecond resistor R2.

The voltage source 100 includes a diode D100, a fifth resistor R5, and acapacitor C100, which are sequentially connected in series to a positiveelectrode of the battery cell 20. The capacitor C100 is electricallyconnected to the positive electrode of the battery cell 20 to maintainthe voltage. The first terminals of the power supply terminal Vcc andthe first resistor R1 are electrically connected to a first terminal ofthe capacitor C100.

In operation, when the battery cell 20 is to be charged, the chargingcontroller 200 outputs the on-level charging control current I200through the charging control terminal CHG. Accordingly, the firsttransistor TR301 is enabled and the second transistor TR302 is disabled.The voltage maintained in the capacitor C100 is applied to the gateterminals of the first and second charging transistors 410 and 420through the first resistor R1 and the first transistor TR301, to enablethe first and second charging transistors 410 and 420.

When the battery cell 20 is separated from the charger 30, the chargingcontroller 200 opens the charging control terminal CHG to change thecharging control current I200 to the off level. Accordingly, the secondtransistor TR302 is enabled and the first transistor TR301 is disabled.A relatively low voltage is applied to the gate terminals of the firstand second charging transistor 410 and 420 through the second transistorTR302. Accordingly, the first and second charging transistors 410 and420 are disabled.

The time constants at which the first and second charging transistors410 and 420 are enabled may be obtained as follows. For example, whenthe resistance value of the first resistor R1 is 10 Kohm and a parallelsum of parasitic capacitances of the first and second chargingtransistors 410 and 420 is 12.8 nF, the time constant is substantiallyobtained as 128 us by the equation: 12.8 nF*10 Kohm. When a parasiticcapacitance component of the first transistor TR301 and a parasiticresistor component are reflected, a greater time constant may beobtained but this value may be significantly less than 51.2 ms. As aresult, according to the present exemplary embodiment, it is possible tosecure enable speeds and disable speeds of the charging transistors 410and 420, even when two or more charging transistors 410 and 420 areemployed.

Although a method for effectively increasing the enable speed anddisable speed of the charging transistor for a charging control has beendescribed, the same principle may be applied to increase the enablespeed and disable speed of a discharging transistor in a dischargingcontrol.

The controllers, converters, and other processing features of theembodiments described herein may be implemented in logic which, forexample, may include hardware, software, or both. When implemented atleast partially in hardware, the controllers, converters, and otherprocessing features may be, for example, any one of a variety ofintegrated circuits including but not limited to an application-specificintegrated circuit, a field-programmable gate array, a combination oflogic gates, a system-on-chip, a microprocessor, or another type ofprocessing or control circuit.

When implemented in at least partially in software, the controllers,converters, and other processing features may include, for example, amemory or other storage device for storing code or instructions to beexecuted, for example, by a computer, processor, microprocessor,controller, or other signal processing device. The computer, processor,microprocessor, controller, or other signal processing device may bethose described herein or one in addition to the elements describedherein. Because the algorithms that form the basis of the methods (oroperations of the computer, processor, microprocessor, controller, orother signal processing device) are described in detail, the code orinstructions for implementing the operations of the method embodimentsmay transform the computer, processor, controller, or other signalprocessing device into a special-purpose processor for performing themethods described herein.

By way of summation and review, various types of battery protectioncircuits have been developed. FIGS. 2A and 2B illustrate two types ofbattery protection circuits.

Referring to FIG. 2A, a battery protective circuit 510 is electricallyconnected between a battery cell 520 and a charger 530. A chargingcontroller 519 supplies a charging control current I500 to a gateterminal of a charging transistor 511. When the charging control currentI500 is at an on level, the charging transistor 511 is enabled by avoltage formed through a resistor R501 to start charging of a batterycell 520 from the charger 530. For example, when the voltage level atwhich the charging transistor 511 is enabled is 11 V, the chargingtransistor 511 may be enabled by setting the charging control currentI500 as 6 uA and the resistor R501 as 2 Mohm, and applying a voltage of12 V to the gate terminal of the charging transistor 511.

When the charging control current I500 is at an off level, the resistorR501 serves to fix a voltage of the gate terminal of the chargingtransistor 511 as a ground voltage. Accordingly, the charging transistor511 is disabled and electrically disconnects the charger 530 and thebattery cell 520.

Referring to FIG. 2B, the battery protective circuit 510 may include acharging transistor 512 to prepare for a Fail where the chargingtransistor 511 is short-circuited. The charging transistors 511 and 512are simultaneously enabled or disabled according to the level of thecharging control current I500.

However, as shown in FIG. 2B, the charging control current I500 isdivided in half and supplied to the charging transistors 511 and 512.Accordingly, a sufficient voltage is not applied to the gate terminalsof the charging transistors 511 and 512. Thus, the charging transistors511 and 512 are not enabled. For example, when the voltage level atwhich charging transistors 511 and 512 are enabled is 11 V, chargingtransistors 511 and 512 may be disabled when a divided current of 3 uAis supplied to each of the transistors 511 and 512 and a voltage of 6 Vis applied to the gate terminals thereof.

Accordingly, the charging transistor 511 may include a resistor R501′ asa pull-down resistor. In this case, the resistor R501′ has a resistancevalue that is twice as much as that of the resistor R501 shown in FIG.2A. Similarly, the charging transistor 512 may include a resistor R502as a pull-down resistor. In this case, the resistor R502 has aresistance value that is twice as much as that of the resistor R501 inFIG. 2A. In this case, for example, even when the divided current of 3uA is supplied to each of the transistors 511 and 512, since resistancevalues of the resistors R501′ and R502 are 4 Mohm, a voltage of 12 V maybe supplied to the gate terminals thereof to enable the chargingtransistors 511 and 512.

However, some problems may occur in an enable speed and disable speed ofthe charging transistors 511 and 512. The enable and disable speeds ofthe charging transistor 511 depend on a time constant caused by theresistor R501′ and a parasitic capacitance component of the chargingtransistor 511. As compared with FIG. 2A, resistor R501′ has aresistance value that is twice as much as that of the resistor R501, anda parasitic capacitance is increased by two times as the chargingtransistor 512 is added. Accordingly, the enable and disable speeds ofthe charging transistor 511 are significantly deteriorated.

For example, when the charging transistor 511 shown in FIG. 2A has aparasitic capacitance component of 6.4 nF, the resistance value of theresistor R501 is 2 Mohm. Accordingly, the time constant is substantiallyobtained as 12.8 ms by 6.4 nF*2 Mohm. However, a parallel sum ofparasitic capacitances of the charging transistors 511 and 512 in FIG.2B is 12.8 nF, and each resistance value of the resistors R501′ and R502is 4 Mohm. Accordingly, the time constant is substantially obtained as51.2 ms by 12.8 nF*4 Mohm. Thus, in the case of FIG. 2B, the timeconstant of the charging transistors 511 and 512 may be 4 times greaterthan that in the case of FIG. 1A.

When the enable and disable speeds deteriorate, it is difficult toobtain proper timing of protective operation of the battery protectivecircuit 510. As a result, the battery protective circuit 510 mayinappropriately perform a protective function.

In accordance with one or more of the aforementioned embodiments, abattery protection circuit is provided that may employ two or morecharging transistors and acquire improved enable and disable speeds.

Example embodiments have been disclosed herein, and although specificterms are employed, they are used and are to be interpreted in a genericand descriptive sense only and not for purpose of limitation. In someinstances, as would be apparent to one of skill in the art as of thefiling of the present application, features, characteristics, and/orelements described in connection with a particular embodiment may beused singly or in combination with features, characteristics, and/orelements described in connection with other embodiments unless otherwiseindicated. Accordingly, it will be understood by those of skill in theart that various changes in form and details may be made withoutdeparting from the spirit and scope of the embodiments set forth in theclaims.

What is claimed is:
 1. A battery protection circuit, comprising: avoltage source; a first resistor including a first terminal connected tothe voltage source; a charging controller to supply a charging controlcurrent through a charging control terminal; a first charging transistorincluding a gate terminal and a first terminal; a second resistorconnected between the gate terminal and the first terminal of the firstcharging transistor; and a current voltage converter connected to asecond terminal of the first resistor to electrically connect thevoltage source to the gate terminal of the first charging transistordepending on the charging control current.
 2. The battery protectioncircuit as claimed in claim 1, further comprising: a second chargingtransistor having a gate terminal and a first terminal; and a thirdresistor connected between the gate terminal and the first terminal ofthe second charging transistor, wherein a second terminal of the secondcharging transistor is electrically connected to the first terminal ofthe first charging transistor, and wherein the gate terminal of thesecond charging transistor is electrically connected to the gateterminal of the first charging transistor.
 3. The battery protectioncircuit as claimed in claim 2, wherein the current voltage converterincludes: a first transistor including a first terminal electricallyconnected to a second terminal of the first resistor; a secondtransistor including a first terminal electrically connected to a secondterminal of the first transistor; and a fourth resistor including afirst terminal electrically connected to a second terminal of the secondtransistor and a second terminal electrically connected to the gateterminal of the first charging transistor, the gate terminal of thesecond charging transistor, and the charging control terminal.
 4. Thebattery protection circuit as claimed in claim 3, wherein: the voltagesource includes a capacitor, and the capacitor is electrically connectedto positive electrode of a battery cell to maintain a voltage.
 5. Thebattery protection circuit as claimed in claim 4, wherein: the chargingcontroller includes a power-supply terminal, and the charging controllerreceives power from the voltage source through the power-supply terminalto generate the charging control current.
 6. The battery protectioncircuit as claimed in claim 5, wherein the voltage source includes adiode and a fifth resistor.
 7. The battery protection circuit as claimedin claim 5, wherein a first terminal of the power-supply terminal andthe first terminal of the first resistor are electrically connected to afirst terminal of the capacitor.
 8. The battery protection circuit asclaimed in claim 7, wherein: the first transistor is enabled when thecharging control current is in an on level and the first chargingtransistor and the second charging transistor are enabled.
 9. Thebattery protection circuit as claimed in claim 8, wherein the secondtransistor is enabled when the charging control current is in an offlevel and the first charging transistor and the second chargingtransistor are disabled.
 10. The battery protection circuit as claimedin claim 3, wherein the second resistor has a resistance value greaterthan that of the fourth resistor.
 11. The battery protection circuit asclaimed in claim 1, wherein the second resistor has a resistance valuegreater than that of the first resistor.
 12. A battery protectioncircuit, comprising: a first resistor connected to a voltage source; afirst charging transistor connected to a battery terminal; a secondresistor connected to the first charging transistor; a controllerconnected to the voltage source to supply a charging control current;and a converter to connect the voltage source to the first chargingtransistor based on the charging control current, wherein the firstresistor has a resistance value less than a resistance value of thesecond resistor and wherein a time constant of the first chargingtransistor is based on the resistance value of the first resistor. 13.The battery protection circuit as claimed in claim 12, furthercomprising: a second charging transistor; and a third resistor connectedto the second charging transistor, wherein a gate terminal of the firstcharging transistor and a gate terminal of the second chargingtransistor are connected to the converter.
 14. The battery protectioncircuit as claimed in claim 13, wherein the resistance value of thefirst resistor is less than a resistance value of the third resistor.15. The battery protection circuit as claimed in claim 13, wherein theconverter includes: a first transistor connected to the first resistor;a second transistor connected between the first transistor and thesecond resistor and the third resistor; and a fourth resistor connectedbetween the controller and gate terminals of the first and secondtransistors.